Method for weld-joining attachment to outer panel of railway vehicle and car body side structure produced by the same

ABSTRACT

A weld-joining structure between an outer panel and an attachment is achieved, which is advantageous in terms of appearance, workability, and cost. To weld-join the outer panel and the attachments including, such as frame members and opening frames and opening frame members, which is a reinforcement or an interior or exterior member for use in the outer panel, the outer panel and the attachment placed on the outer panel are weld-joined by laser welding at overlapping portions of the outer panel and the attachment. The laser welding is performed along a polishing mark formed in one direction on an externally exposed-side surface of the outer panel and the attachment.

TECHNICAL FIELD

The present invention relates to a method for weld-joining an attachmentto an outer panel of a railway vehicle. In particular, the inventionrelates to a method for weld-joining an attachment to an outer panel ofa railway vehicle, the method being carried out such that theattachment, such as a frame member, an opening frame, and an openingframe member, which is a reinforcement or an interior or exterior memberfor use in the outer panel, is weld-joined to the outer panel. Theinvention also relates to a car body side structure produced by themethod.

BACKGROUND ART

In one known structure for reinforcing an outer panel of a railwayvehicle, vertically and horizontally arranged frame members are placedon and weld-joined to the interior surface of the outer panel toreinforce the outer panel (see, for example, Patent Document 1). Inanother exemplary structure, vertical and horizontal frame members b andc are disposed on and weld-joined to an outer panel a, as shown in FIGS.6A and 6B. In these structures, spot welding shown in FIG. 7A is usedfor weld-joining. However, since a load of 1 t is applied during thespot welding process, indentations are formed on the exterior surface,resulting in the deterioration of the appearance. In addition, much timeand labor are required for joining, and the cost increases. Since alarge load is applied, a large apparatus is required, and an expensivecopper-made electrode plate d must be used, so that the cost for theequipment is high.

In view of the above, in one known method, laser welding shown in FIG.7B is used for weld-joining (see, for example, Patent Document 2).

-   [Patent Document 1] Japanese Patent Application Laid-Open No. Hei.    9-30414.-   [Patent Document 2] Japanese Patent No. 2843899.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present inventor has conducted various experiments and studies onweld-joining of attachments to the outer panels of stainless steel-madevehicles by means of laser welding. The inventor has noticed that, whenframe members b and c are placed on the interior surface of an outerpanel a and laser-welded thereto in a direction shown by an arrow f witha laser beam e directed from the interior side as shown in FIG. 5, alinear mark g along the laser welding line is formed on the exteriorsurface of the outer panel a in some cases. This is because, with laserwelding, the penetration depth of a fused portion serving as a joiningportion h is small in the outer panel a, as shown in FIG. 7B. Therefore,a strong force is exerted on the frame member b and c side duringsolidification, so that the outer panel a having a thickness of about1.5 to 3 mm and the frame members b and c having a thickness of about 1to 2.5 mm are slightly bent along the laser welding line. The linearmark g was less noticeable on mirror surfaces but was more noticeable onsurfaces having polishing marks j, which are a type of decorative marksprovided to make flaws and stains less noticeable as shown in FIG. 5, inspecific cases. The inventors have found that, in the above specificcases, the laser welding line intersects the polishing marks j, and thatthe linear mark g is totally unnoticeable when laser welding isperformed such that the laser welding line is along the polishing marksj. A similar tendency may be observed in other metal plates such asaluminum plates.

In the structure described in Patent Document 1, since the vertical andhorizontal frame members are laser welded to the outer panel, theformation of the linear mark g on the decorative surface can not beavoided. In addition, the horizontal frame members are divided by thevertical frame members, so that the welding cannot be performed in acontinuous manner. In view of the above, the present inventor hascompleted an inventive method for weld-joining attachments to an outerpanel of a railway vehicle, in which the outer panel having polishingmarks formed in a specific direction is used. The present inventor hasalso completed a car body side structure produced by the method. Themethod and the car body side structure are advantageous in terms ofappearance, workability, and cost.

It is an object of the present invention to provide a method forweld-joining attachments to an outer panel of a railway vehicle, whichis advantageous in terms of appearance, workability, and cost, and toprovide a car body side structure produced by the same, which areobtained as a result of vigorous efforts of the inventor.

Means for Solving the Problems

To achieve the above object, the present invention provides a method forweld-joining an attachment to an outer panel of a railway vehicle, inwhich the attachment, such as a frame member, an opening frame, and anopening frame member, which is a reinforcement or an interior orexterior member for use in the outer panel, is weld-joined to the outerpanel. The method is mainly characterized by laser welding, at anoverlapping portion of the outer panel and the attachment placed on theouter panel, the outer panel and the attachment along a polishing markformed in one direction on an externally exposed-side surface of theouter panel and the attachment to weld-join the outer panel and theattachment.

In the above configuration, for example, the frame member that is one ofthe attachments is placed on the interior surface of the outer panel andweld-joined such that the outer panel is disposed on the exterior side.Furthermore, the opening frame and the opening frame member that areones of the attachments are placed on the exterior surface of the outerpanel and weld-joined such that the opening frames and the opening framemembers are disposed on the exterior side. In this case, when theattachments are placed on and weld-joined to the outer panel at theiroverlapping portions by laser welding from the interior side, the laserwelding is performed along the polishing marks formed on theexterior-side surfaces of the outer panel and the attachments.Therefore, the formation of noticeable linear marks in the laser weldingdirection on the exterior surfaces can be avoided, and laser welding forweld-joining the attachments to the outer panel can be put to practicaluse. As described above, the attachments are weld-joined to the outerpanel at the overlapping portions by laser welding from the interiorside, and the laser welding is performed along the polishing marksformed on the exterior-side surfaces of the outer panel and theattachments, so that the formation of noticeable linear marks in thelaser welding direction on the exterior surfaces can be avoided. Sincethe laser welding can be performed without deterioration of appearance,the workability is improved accordingly, and the cost is also reduced.

In another configuration, the polishing mark on the outer panel isformed in a lengthwise direction of the vehicle, and the frame member ishorizontally placed on an interior surface of the outer panel. The outerpanel and the frame member are weld-joined by laser welding performed ina lengthwise direction of the frame member. Since the direction of thepolishing mark on the outer panel is set to the lengthwise direction ofthe vehicle, a large number of long horizontal frame members that can becontinuously laser welded can be used. This contributes to the requiredcar body strength. In this manner, the ratio of the number of longhorizontal frame members can be increased, and the ratio of thecontinuously laser welded portions along the horizontal frame memberscan thereby be increased. This is further advantageous in terms ofworkability and cost reduction and contributes to the required car bodystrength.

In another configuration, the frame member is vertically placed on theinterior surface of the outer panel, and the outer panel and the framemember are weld-joined by spot welding. Linear marks are formed whenlaser welding is performed along the vertical frame member. Since spotwelding is used to weld-join the vertical frame member to the outerpanel having the polishing mark formed in the lengthwise direction ofthe vehicle, the formation of noticeable linear marks intersecting thepolishing mark can be avoided. In this manner, the number of thevertical frame members can be reduced by an amount that corresponds tothe increase in the number of the horizontal frame members. Even in sucha case, the required car body strength can be ensured.

In another configuration, the vertical frame member and the horizontalframe member are weld-joined together by any of plug welding, spotwelding, and laser welding. Since any suitable one of various weldingmethods can be used, the vertical and horizontal frame members can beweld-joined together without affecting the outer panel and theappearance, and the joint strength between the vertical and horizontalframe members can be improved.

With the above method for weld-joining an attachment to an outer panelof a railway vehicle, a car body side structure of a railway vehiclehaving the following characteristic configuration is provided while theadvantageous features of the above methods are effectively utilized. Theouter panel having a polishing mark formed in the lengthwise directionof the vehicle and a frame member horizontally placed on the interiorsurface of the outer panel are joined at a weld-joining portion weldedby laser welding performed in the lengthwise direction of the horizontalframe member. The outer panel and a frame member vertically placed onthe interior surface of the outer panel are joined at a weld-joiningportion welded by spot welding. An opening frame or an opening framemember having a lengthwise polishing mark formed on an exterior surfacethereof is placed on an exterior surface of an opening edge of the outerpanel. The opening frame or the opening frame member is joined to theouter panel at a weld-joining portion welded by laser welding performedin the lengthwise direction of the opening frame or the opening framemember.

In another configuration, the outer panel includes an opening for awindow and an opening for an entrance door. The horizontal frame membersare disposed at substantially regular vertical intervals on the interiorsurface of the outer panel except for the openings for the window andthe entrance door. The vertical frame members are disposed along sideportions of the openings for the window and the entrance door and alongan end portion of the outer panel. Between the vertical frame members, avertical reinforcing member is placed on the horizontal frame membersfrom an interior side so as to extend therebetween and is joined theretoat weld-joining portions welded by any of plug welding, spot welding,and laser welding. In this case, in areas where the horizontal framemembers can be disposed, a higher priority is given to the horizontalframe members than to the vertical frame members so that the number ofthe horizontal frame members disposed in those areas is greater than thenumber of the vertical frame members. In this manner, the horizontalframe members are prevented from being divided by the vertical framemembers, and the continuity of laser welding is maintained. Therefore,the required car body strength can be ensured by the vertical framemembers significantly reduced in their number and by the verticalreinforcing members that can be weld-joined by any suitable one ofvarious welding methods without affecting the outer panel and theappearance. Specifically, the reinforcing members are not welded to andnot in contact with the outer panel while they are arranged in aseparating state with respect to the outer panel. Therefore, thestrength to resist out-of-plane deformation caused by the in-plane shearforce in the outer panel can be improved.

For this purpose, preferably, the horizontal frame members have ahat-shaped cross-section and include flanges on both sides thereof thatare weld-joined to the outer panel. In addition, preferably, thevertical reinforcing member includes a notch that fits a rear portion ofthe flange of the horizontal frame member. The vertical reinforcingmember with the notches is placed on and weld-joined to the flanges ofthe horizontal frame members.

Other objects and features of the present invention will be apparentfrom the following detailed description when read in conjunction withthe drawings. Each of the features of the present invention may be usedalone or in various practicable combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D show an example of the joining structure between an outerpanel, vertically and horizontally arranged frame members, openingframes, and opening frame members, the joining structure being used in acar body side structure of a railway vehicle according to an embodimentof the present invention, FIG. 1A being a front view from the innerside, FIG. 1B being a cross-sectional view taken along line B-B in FIG.1A, FIG. 10 being a cross-sectional view taken along line C-C in FIG.1A, FIG. 1D being an enlarged view of area E in FIG. 1C.

FIG. 2 is a horizontal cross-sectional view between the window and theentrance door of the car body side structure in FIG. 1A.

FIG. 3 is a horizontal cross-sectional view illustrating a laser weldingfacility used for welding of the weld-joining portions in theembodiment.

FIGS. 4A and 4B show the laser welding facility shown in FIG. 3, FIG. 4Abeing a plan view, FIG. 4B being a front view.

FIG. 5 is a perspective view illustrating an example of the condition ofa weld-joining portion between an outer panel and a frame memberweld-joined by conventional laser welding.

FIGS. 6A and 6B show an example of the joining structure between anouter panel, vertically and horizontally arranged frame members, openingframes, and opening frame members, the joining structure being used in aconventional car body side structure of a railway vehicle, FIG. 6A beinga front view from the inner side, FIG. 6B being a cross-sectional viewtaken along line A-A in FIG. 6A.

FIGS. 7A and 7B are cross-sectional views illustrating weld-joinedconditions of spot welding and laser welding.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1A to 4B, an embodiment of a method forweld-joining attachments to an outer panel of a railway vehicleaccording to the present invention and an embodiment of a car body sidestructure produced by the inventive method are specifically described tofacilitate understanding of the invention.

In one embodiment, a car body side structure 41 shown in FIGS. 1A to 1Dand 2 is produced. Specifically, attachments are weld-joined to astainless steel-made outer panel 3 shown in FIG. 2. The attachmentsinclude: stainless steel-made frame members 1 and 2 vertically andhorizontally arranged to reinforce the outer panel 3; and stainlesssteel-made opening frames and opening frame members 42 a and 43 a usedas exterior members disposed on opening edges for an entrance door 42and a window 43. However, the present invention is not limited to theabove embodiment and is applicable to any car body structure includingan outer panel of a railway vehicle and attachments weld-joined to theouter panel. In addition, the material is not particularly limited tostainless steel.

As shown in FIG. 2, the frame members 1 and 2, being the attachments,are placed on the interior surface of the outer panel 3 and weld-joinedsuch that the outer panel 3 is disposed on the exterior side. Theopening frame and opening frame member 42 a and 43 a, being theattachments, are placed on the exterior surface of the outer panel 3 andweld-joined such that the opening frame and opening frame member 42 aand 43 a are disposed on the exterior side. As described above, in thepresent embodiment, the attachments including the frame members 1 and 2and the opening frame and opening frame member 42 a and 43 a, which arereinforcements or as interior and exterior members for use in the outerpanel, are weld-joined to the outer panel 3 at weld-joining portions 4,5, and 45 shown in FIGS. 1A and 2. More specifically, the attachmentsincluding the frame members 1 and 2 and the opening frame and openingframe member 42 a and 43 a are placed on and weld-joined to the outerpanel 3 at their overlapping portions by laser welding performed alongpolishing marks formed in one direction on the externally exposed-sidesurfaces of the outer panel 3 and the attachments 1, 2, 42 a, and 43 a.A YAG laser beam is suitable for the laser beam used for stainlesssteel. However, the laser beam is not limited thereto.

As described above, the attachments including the frame members 1 and 2and the opening frame and opening frame member 42 a and 43 a are placedon and weld-joined to the outer panel 3 at their overlapping portions bylaser welding from the interior side. In this case, the laser welding isperformed along the polishing marks formed in one direction on theexterior-side surfaces of the outer panel 3 and the attachments 1, 2, 42a, and 43 a. Therefore, the formation of noticeable linear marks in thelaser welding direction on the exterior surfaces can be avoided, andlaser welding for weld-joining the attachments including the framemembers 1 and 2 and the opening frame and opening frame member 42 a and43 a to the outer panel 3 can be put to practical use. In this manner,the laser welding lines are formed along the polishing marks on theexterior-side surfaces. Therefore, the formation of noticeable linearmarks in the laser welding direction on the exterior surfaces can beavoided. Since laser welding can be performed without deterioration ofappearance, the workability is improved accordingly, and the cost isalso reduced. Preferably, in terms of the joining strength and theappearance of the outer panel 3, the depth of penetration t into theouter panel 3 during laser welding is 0.1 mm to about 50% of thethickness of the outer panel 3.

In the present embodiment, the outer panel 3 used has polishing marksformed in the lengthwise direction of the vehicle, and the frame members2 are horizontally placed on the interior surface of the outer panel 3as shown in FIGS. 1A and 2 and are joined thereto by laser welding atthe weld-joining portions 5 continuous in the lengthwise direction ofthe frame members 2. Since the direction of the polishing marks on theouter panel 3 is set to the lengthwise direction of the vehicle, a largenumber of long horizontal frame members 2 can be used as shown in FIG.1A and can be continuously laser welded. This contributes to therequired car body strength. In other words, the ratio of the number oflong horizontal frame members 2 is increased, and the ratio of thecontinuously laser welded portions is also increased. This is furtheradvantageous in terms of workability and cost reduction and contributesto the required car body strength.

Meanwhile, the frame members 1 vertically placed on the interior surfaceof the outer panel 3 are weld-joined to the outer panel 3 at theweld-joining portions 4 by spot welding as shown in FIG. 1 a. Linearmarks are formed when laser welding is performed along the verticalframe members 1. Since spot welding is used to weld-join the verticalframe members 1 to the outer panel 3 having the polishing marks formedin the lengthwise direction of the vehicle, the formation of noticeablelinear marks intersecting the polishing marks can be avoided. In thismanner, the number of the vertical frame members 1 can be reduced by anamount that corresponds to the increase in the number of the horizontalframe members 2. Even in such a case, the required car body strength canbe ensured.

The vertical frame members 1 and the horizontal frame members 2 areweld-joined at the weld-joining portions 6 by any of plug welding, spotwelding, and laser welding. Since any suitable one of various weldingmethods can be used, the vertical and horizontal frame members 1 and 2can be weld-joined together without affecting the outer panel 3 and theappearance, and the joint strength between the frame members 1 and 2 canbe improved.

With the above method for weld-joining the attachment to the outerpanel, the outer panel 3 having the polishing marks formed in thelengthwise direction of the vehicle and the frame members 2 horizontallyplaced on the interior surface of the outer panel 3 are joined at theweld-joining portions 5 welded by laser welding performed in thelengthwise direction of the frame members 2. The outer panel 3 and theframe members 1 vertically placed on the interior surface of the outerpanel 3 are joined at the weld-joining portions 4 welded by spotwelding. Moreover, the opening frame and opening frame member 42 a and43 a are placed on the exterior surfaces of the opening edges of theouter panel 3, which are provided for the entrance door 42 and thewindow 43, and are joined to the outer panel 3 at the weld-joiningportions 45 welded by laser welding performed in the lengthwisedirections of the opening frame and opening frame member 42 a and 43 a.In this manner, the car body side structure 41 of a railway vehicle isobtained. The opening frame and opening frame member 42 a and 43 a havepolishing marks formed in their lengthwise directions on the exteriorsurfaces, i.e., along their peripheries. Therefore, the advantageousfeatures of the above method are effectively utilized, and sufficientcar body strength can be ensured at low cost while the appearance is notimpaired. In the standard procedure for producing the car body sidestructure 41, an outer panel 3 having a size corresponding to thedistance between the entrance doors 42 and including an opening for thewindow 43 is used, and the opening frame 43 a is placed on andweld-joined to the exterior-side edge of the opening for the window 43.Subsequently, the vertical and horizontal frame members 1 and 2 areplaced on and weld-joined to the interior surface of the outer panel 3,and reinforcing members 46 are placed on and weld-joined to thehorizontal frame members 2. A plurality of such outer panels 3 areseparately produced. Then, the opening frame members 42 a are placed onand weld-joined to the edges of the openings for the entrance doors,whereby the outer panels 3 are joined together so as to have a lengthcorresponding to the length of one vehicle.

In the car body side structure 41 shown in FIGS. 1A to 1D and 2, thehorizontal frame members 2 are disposed at substantially regularvertical intervals on the interior surface of the outer panel 3 exceptfor the openings for the window 43 and the entrance doors 42, inparticular, as shown in FIGS. 1A to 1D. The vertical frame members 1 aredisposed along the side portions of the openings for the window 43 andthe entrance doors 42 and along the edge portions (not shown) of theouter panel 3. Between the vertical frame members 1, the verticalreinforcing members 46 are placed on the horizontal frame members 2 fromthe interior side so as to extend therebetween and are joined thereto atweld-joining portions 47 welded by any of plug welding, spot welding,and laser welding. In areas where the horizontal frame members 2 can bedisposed, a higher priority is given to the horizontal frame members 2than to the vertical frame members 1, so that the number of thehorizontal frame members 2 disposed in those areas is greater than thenumber of the vertical frame members 1. In this manner, the horizontalframe members 2 are prevented from being divided by the vertical framemembers 1, and the continuity of laser welding is maintained. Therefore,the required car body strength can be ensured by the vertical framemembers 1 significantly reduced in their number and by the verticalreinforcing members 46 that can be weld-joined by any suitable one ofvarious welding methods without affecting the outer panel 3 and theappearance. Specifically, the reinforcing members are not welded to andnot in contact with the outer panel while they are arranged in aseparating state with respect to the outer panel. Therefore, thestrength to resist out-of-plane deformation caused by the in-plane shearforce in the outer panel can be improved. For this purpose, thestructures shown in the figures are preferred. More specifically, insuch structures, the horizontal frame members 2 have a hat-shapedcross-section, and the flanges 2 b on both sides are weld-joined to theouter panel 3. In addition, each vertical reinforcing member 46 has ahat-shaped cross-section and includes flanges 46 a and notches 46 b thatfit the rear portions of the flanges 2 b of the horizontal frame members2. The vertical reinforcing member 46 is weld-joined to the flanges 2 bof the horizontal frame members 2 with the flanges 46 a abutting againstthe flanges 2 b.

In areas where the vertical frame members 1 interfere with thehorizontal frame members 2 having a higher priority for continuousplacement, the vertical frame members 1 are disposed in a dividedmanner. However, since the vertical frame members 1 are spot-welded tothe outer panel 3 in a discontinuous manner, the workability is notparticularly affected.

The laser welding described above is performed using, for example, alaser welding facility shown in FIGS. 3, 4A, and 4B. As shown in FIGS.4A and 4B, this laser welding facility includes a welding operation unit11 and left and right jig trucks 13 and 14 that travel on rails 12extending across the welding operation unit 11 in the left and rightdirections. Each of the left and right jig trucks 13 holds an outerpanel 3 that forms a car body structure of a vehicle such as the carbody side, roof, or end. The left and right jig trucks 13 and 14 enterthe welding operation unit 11 in an alternate manner to laser-weld theheld outer panel 3 to frame members 1 and 2 to be vertically andhorizontally arranged thereon, and this procedure is repeated. Everytime the left and right jig trucks 13 and 14 exit from the weldingoperation unit 11, the welded car body structure placed thereon isreplaced with a new outer panel 3. The welding operation unit 11includes a gate-shaped operation leg 16 that travels on rails 15. Theoperation leg 16 supports an articulated robot 17 having, for example,about five joints. The frame members 1 and 2 to be vertically andhorizontally arranged are laser welded to the outer panel 3 placed onthe jig truck 13 entering the welding operation unit 11 through the useof the articulated robot 17. As shown in FIG. 3, the articulated robot17 is provided with a laser torch 18 for laser welding disposed at theend portion of the robot arm. The laser torch 18 supplies a laser beamfrom a laser oscillating device 19 provided with a cooling mechanismthrough an optical fiber, and the weld-joining portions are irradiatedwith the laser beam to perform laser welding in a predetermined manner.The welding operation unit 11 further includes two pressurizingmechanisms 21 for laser welding on the left and right sides thereof. Thepressurizing mechanisms 21 apply downward pressure to the outer panelplaced on the jig truck 13 or 14 entering the welding operation unit 11and to the frame members 1 and 2 to be vertically and horizontallyarranged on the outer panel and support them in predetermined positionsfor laser welding. Each of the left and right pressurizing mechanisms 21includes a pair of pressurizing rods 24 supported by a gate-shapedsupporting leg 23 traveling on rails 22, and the pressurizing andsupporting operation is performed using the left and right pairs ofpressurizing rods 24. The laser welding operation is controlled by arobot control unit 31 and a jig control unit 32 that are operatedcooperatively.

As shown in FIGS. 1A and 2, the vertically and horizontally arrangedfirst and second frame members 1 and 2 are weld-joined to the outerpanel 3 with an end portion 2 a of each second frame member 2 facing aside surface of a corresponding one of the first frame members 1. Toreinforce the outer panel 3, each first frame member 1 is placed in astraddling manner on the outer panel 3 and the end portions 2 a of thesecond frame members 2 weld-joined to the outer panel 3 at theweld-joining portions 5 and is weld-joined to both the second framemembers 2 and the outer panel 3 at the weld-joining portions 6 and 4 inthe manner shown in FIG. 2. As described above, each first frame member1 is placed in a straddling manner on the outer panel 3 and the endportions 2 a of the second frame members 2 weld-joined to the outerpanel 3 and is weld-joined to both the second frame members 2 and theouter panel 3. Therefore, the entire end portion 2 a of each secondframe member 2 has a structure that is to be weld-joined to the outerpanel 3 and is disposed below the first frame member 1 in an overlappingmanner while the three-dimensional structural shapes of both the framemembers utilizing the material and structural characteristics aremaintained. This entire end portion 2 a of the second frame member 2 isalso weld-joined to the first frame member 1 weld-joined to the outerpanel 3. Furthermore, the horizontal frame members 2 can be continuouslylaser welded to the outer panel 3. In this manner, the concentration ofstress on the end portion 2 a of the second frame member 2 can beprevented while the joint strength between the vertically andhorizontally arranged first and second frame members 1 and 2 isimproved.

More specifically, as shown in FIGS. 1A to 1D and 2, each second framemember 2 has a hat-shaped cross-section, and the flanges 2 b on bothsides of the second frame member 2 are placed on and weld-joined to theouter panel 3 by laser welding. As shown in the example in FIGS. 1A and2, each first frame member 1 has a hat-shaped cross-section and includesflanges 1 b on both sides thereof. The first frame member 1 is disposedin a straddling manner on the outer panel 3 and the end portions 2 a ofthe second frame members 2. More specifically, one of the flanges 1 b isplaced on and weld-joined to the end portions 2 a of the second framemembers 2 by any of laser welding, spot welding, and the plug weldingdescribed above, and the other flange 1 b is placed on and weld-joinedto the outer panel 3 by laser welding. With this configuration, thevertically and horizontally arranged frame members 1 and 2 can be joinedto the outer panel 3 by laser welding. In addition, the vertically andhorizontally arranged frame members 1 and 2 are mutually joined andjoined to the outer panel in an improved manner, and the joint strengthand the joining strength can be improved by effectively utilizing themechanical shapes of the frame members 1 and 2.

In railway vehicles, the outer panel 3 is often reinforced by the longhorizontal frame members 2 extending in the lengthwise direction, as inthe car body side structure 41 shown in FIGS. 1A and 2. In such a case,the vertical frame members 1 disposed along the openings for the window43 and the entrance doors 42 have side surfaces facing the end portions2 a of a large number of horizontal frame members. Therefore, the jointstrength between these frame members and the joining strength betweenthe outer panel 3 and these frame members are important issues. Toimprove the joint strength and the joining strength, the specificexample shown in FIGS. 1A to 1D and 2 is effective. In addition, thelaser weld-joined portions 4 continuous along the openings for thewindow 43 and the entrance doors 42 preferably serves as a waterproofmeasure to prevent rainwater from entering through the openings. Asshown in FIG. 2, the vertical frame members 1 disposed along theopenings for the window 43 and the entrance door 42 are independent ofthe opening frame and opening frame member 42 a and 43 a disposed in theopenings for the window 43 and the entrance doors 42. For example, ifthe opening frame member 43 a, the frame member 1, and the outer panel 3are laser welded together at their three-layer overlapping portion, thelaser welding takes a long time. However, since the opening frame member43 a and the frame member 1 are laser welded to the outer panel 3 in anindependent manner, the above problem can be avoided. In this case, thelaser welding line of the frame member 1 adjacent to the opening framemember 43 a is noticeable since the laser welding line is orthogonal tothe polishing marks on the outer panel 3 that are formed in thelengthwise direction of the vehicle. However, this laser welding linecan be covered and hidden by the opening frame member 43 a that isplaced on the exterior surface of the outer panel 3 and laser weldedfrom the inner side. Even when not covered and hidden, the laser weldingline can be less noticeable by placing it near the edge of the openingframe member 43 a. Since an enough space is not provided, the openingframe member 42 a and the frame member 1 are laser welded to the outerpanel 3 from the interior side with the three members overlapping witheach other. However, to simplify the joining, spot welding may be used.The frame members 1 and the opening frame and opening frame member 42 aand 43 a may be formed integrally and used as an integrated member. Alsoin this manner, the joint strength and the joining strength can beimproved.

INDUSTRIAL APPLICABILITY

In the present invention, the outer panels of a railway vehicle can bejoined to frame members, opening frames, opening frame members, andother members by laser welding without deterioration of the appearance.Therefore, the present invention is advantageous in terms of weldingworkability, cost, strength, appearance, and the like.

The invention claimed is:
 1. A method for weld-joining an attachment toan outer panel of a railway vehicle, the method comprising: providingthe outer panel having a polishing mark formed in one direction on anexterior surface of the outer panel; providing the attachment as atleast one of a reinforcement, an interior member, and exterior memberfor use in the outer panel, the attachment including a frame member, anopening frame, and an opening frame member; and placing the attachmenton an interior surface of the outer panel such that at least a portionof the outer panel and a portion of the attachment overlap with eachother to form an overlapping portion, and laser welding, from theinterior surface, the outer panel and the attachment together at theoverlapping portion and along the polishing mark of the outer panel. 2.The method according to claim 1, wherein one of the opening frame andthe opening frame member is placed on an external surface of an openingedge of the outer panel, and the outer panel and the one of the openingframe and the opening frame member are weld-joined by laser welding in alengthwise direction of the one of the opening frame and the openingframe member.
 3. The method according to claim 1, wherein the polishingmark on the outer panel is formed in a lengthwise direction of thevehicle, and the frame member is horizontally placed on an interiorsurface of the outer panel so that the outer panel and the frame memberare weld-joined by laser welding in a lengthwise direction of the framemember.
 4. The method according to claim 3, wherein the outer panel andthe opening frame or the opening frame member placed on an exteriorsurface of an opening edge of the outer panel are weld-joined by laserwelding in a lengthwise direction of the opening frame or the openingframe member.
 5. The method according to claim 3, wherein the framemember includes a vertical frame member vertically placed on theinterior surface of the outer panel, and the outer panel and thevertical frame member are weld-joined by spot welding.
 6. The methodaccording to claim 5, wherein the vertical frame member and thehorizontal frame member are weld-joined together by any of plug welding,spot welding, and laser welding.
 7. The method according to claim 5,wherein the outer panel and the opening frame or the opening framemember placed on an exterior surface of an opening edge of the outerpanel are weld-joined by laser welding in a lengthwise direction of theopening frame or the opening frame member.
 8. A car body side structureof a railway vehicle, comprising: an outer panel, a vertical framemember and a horizontal frame member, and one of an opening frame and anopening frame member, the vertical frame member and the horizontal framemember being placed on an interior surface of the outer panel, the outerpanel being weld-joined to the vertical frame member, the horizontalframe member, and the one of the opening frame and the opening framemember, wherein the outer panel has a polishing mark formed in alengthwise direction of the vehicle, the outer panel being joined to thehorizontal frame member at a weld-joining portion that is laser weldedat the interior surface of the outer panel and along the polishing markin a lengthwise direction of the horizontal frame member, the outerpanel is joined to the vertical frame member at a weld joining portionwelded by spot welding, and the one of the opening frame and the openingframe member has a lengthwise polishing mark formed on an exteriorsurface thereof and is placed on an exterior surface of an opening edgeof the outer panel, the outer panel and the one of the opening frame andthe opening frame member being joined at a weld joining portion weldedby laser welding performed in a lengthwise direction of the one of theopening frame and the opening frame member.
 9. The car body sidestructure of a railway vehicle according to claim 8, wherein the outerpanel, the frame member, and the one of the opening frame and theopening frame member are made of stainless steel.
 10. The car body sidestructure of a railway vehicle according to claim 8, further comprising:the outer panel including an opening for a window and an opening for anentrance door; the horizontal frame members are disposed atsubstantially regular vertical intervals on the interior surface of theouter panel except for the openings for the window and the entrancedoor; the vertical frame members are disposed along side portions of theopenings for the window and the entrance door and along an end portionof the outer panel; and between the vertical frame members, a verticalreinforcing member is placed on the horizontal frame members from aninterior side so as to extend therebetween and is joined thereto atweld-joining portions welded by any of plug welding, spot welding, andlaser welding.
 11. The car body side structure of a railway vehicleaccording to claim 10, wherein the outer panel, the frame members, andthe one of the opening frame and the opening frame member are made ofstainless steel.
 12. The car body side structure of a railway vehicleaccording to claim 8, wherein the vertical frame member and thehorizontal frame member are weld-joined at a weld-joining portiontogether by any of plug welding, spot welding, and laser welding. 13.The car body side structure of a railway vehicle according to claim 12,wherein the outer panel, the frame members, and the one of the openingframe and the opening frame member are made of stainless steel.
 14. Thecar body side structure of a railway vehicle according to claim 12,wherein: the outer panel includes an opening for a window and an openingfor an entrance door; the horizontal frame members are disposed atsubstantially regular vertical intervals on the interior surface of theouter panel except for the openings for the window and the entrancedoor; the vertical frame members are disposed along side portions of theopenings for the window and the entrance door and along an end portionof the outer panel; and between the vertical frame member, a verticalreinforcing member is placed on the horizontal frame members from aninterior side so as to extend therebetween and is joined thereto atweld-joining portions welded by any of plug welding, spot welding, andlaser welding.
 15. The car body side structure of a railway vehicleaccording to claim 10, wherein the horizontal frame members have ahat-shaped cross-section and include flanges on both sides thereof thatare weld-joined to the outer panel; and the vertical reinforcing memberincludes a notch that fits a rear portion of the flange of thehorizontal frame member and the vertical reinforcing member is placed onand weld-joined to the flanges of the horizontal frame members.
 16. Thecar body side structure of a railway vehicle according to claim 15,wherein the outer panel, the frame members, and the one of the openingframe and the opening frame member are made of stainless steel.